The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Motor assemblies for aircrafts generally including a nacelle forming a generally circular outer envelope, comprising inside a turbojet engine disposed along the longitudinal axis of this nacelle.
The turbojet engine receives fresh air coming from the upstream or front side, and rejects, from the downstream or back side, the hot gases issued from the combustion of fuel, which give a certain thrust. For bypass turbojet engines, fan blades disposed around this turbojet engine generate a significant secondary flow of cold air along an annular flow path passing between the engine and the nacelle, which adds a high thrust.
Nacelles may include a thrust reverser system which closes at least partially the annular flow path of cold air, and rejects the secondary flow forward in order to generate a braking thrust of the aircraft.
Some thrust reversers include downstream movable cowls which can slide axially backward under the effect of actuators, by deploying flaps in the annular flow path in order to close at least partially this flow path. The flaps return the cold air flow radially outward through gates that have been uncovered during this sliding, comprising blades which direct this flow forward.
In particular, the reverser may include a single cowl also called “O-duct,” forming a shroud transversely forming a complete circle. Alternatively the thrust reverser may include two cowls symmetrically disposed relative to a vertical plane, each forming a semi-circle, also called “D-duct,” thereby constituting a complete shroud.
The backward movement of the cowls is performed by control cylinders of the thrust reverser for the normal operation of the reverser, or to access to the internal portions of the nacelle in order to perform maintenance operations on the motor.
Each cowl includes an inner panel supported and axially guided by a primary rail longitudinally disposed in the nacelle, comprising a movable portion connected to the cowl, sliding on a fixed portion connected to the upstream structure. These primary rails have a high resistance to practically support the whole mass as well as the different stresses applied to the reverser during its operation.
The cowls also include secondary guide rails of the front portion of the outer panel of these cowls, which is cantilevered above the flow reversal gates, to inhibit bending of these portions.
Some “D-duct”-type half-cowls include two control cylinders fixed to an upper point and a lower point of each cowl, the two cowls not being connected to each other by an upper connection. In the event of absence or failure, during the flight, of the upper cylinder of a cowl that is open, the upper portion of this cowl is no longer sufficiently held to withstand the mass and the significant pressures exerted above. This cowl may be deformed or tilt with a backward movement of its upper portion, enough to dislocate the secondary rail.
The same issue may occur in the event of an absence or a failure of the lower cylinder, if the two cowls do not include a lower connection between the both of them. It can also be obtained with cowls maintained by three cylinders, if the assembly does not include a high rigidity.
In the same way, in the event of an absence or failure of the control cylinder, a single “O-duct”-type cowl may also be deformed or tilt enough to dislocate the secondary rail.
To address this disengagement issue of the secondary rail, it is known to place an end-of-travel stop on this rail in order to inhibit its dislocation in the event of a significant backward movement of the supported cowl.
Nonetheless, the secondary rails generally comprising a lightweight structure sufficient to a guiding of the outer portions of the cowls during the opening of the reverser, for its operation or for maintenance operations, are not intended to withstand high axial loads applied on an end-of-travel stop fixed on these rails, which may occur in the event of an absence or failure of a cylinder, during the operation of the thrust reverser.